An alternative approach of synthesizing silver nanoribbon from waste X-ray films using purified gelatinase secreted by Paenibacillus thiaminolyticus CH4

The present study describes an unconventional and improved approach to synthesizing silver nanoribbons from waste X-ray films using gelatinase purified from Paenibacillus thiaminolyticus CH4, isolated from cattle hide. Optimization of gelatinase production from P. thiaminolyticus CH4 showed highest production at pH 8.0, 37 °C temperature, 1.0% (w/v) starch, 0.5% (w/v) casein and 0.5% (w/v) NaCl and an incubation time of 72 h. Gelatinase was purified by ammonium sulfate (60%) precipitation followed by dialysis and Sephacryl S-200 gel-filtration chromatography with a recovery of 28% and 2.6-fold purification. The molecular weight of the purified enzyme was 98 kDa with a dimeric configuration. The zymogram confirmed gelatin hydrolysis. The purified gelatinase was stable between pH 7.0–9.0 and temperature 4–37 °C with optimum activity at pH 7.0–8.0 and 37 °C. Gelatinase produced well-dispersed silver nanoribbons (15–45 nm) from waste X-ray films with 92.92 wt % silver element. The UV–visible spectra of silver nanoribbons showed a characteristic absorbance peak at 380–400 nm. FTIR results confirmed that the functional groups of gelatin acted as reducing and capping agents in silver nanoribbon formation. The gelatinase used in the present study produced smaller-sized nanoribbons with a higher amount of extracted silver. The enzyme can further be used to develop a sustainable industrial process for the bioconversion of waste X-ray films into valuable silver.